Lecture 7: Industrial minerals & Fossil fuels

Building stones

1. Granite - coarse grained and hardwearing

2. Sandstone - quartz and feldspar

3. Limestone/Dolomite - CaCO3 - MgCO3

4. Marble - metamorphosed limestone

5. Slate - clays compressed during metamorphism

What are crushed rocks?

Aggregates:

• largest volume hard-rock mineral commodity

• building foundations and road building

• easy to mine and crush but hard and inert

• most countries have plentiful supply

• mined openpit in quarries

Sand and gravel

• concrete production and road building

• weathered or abraded by glaciers from parent rock and transported by water

• found in river chanels, their floodplains and alluvial fans and glacial deposits

• exploited through dredging

Cement

• chemical binder

• mixed with sand to make mortar

• sand and gravel to make concrete

• cement plants usually located near limestone quarries

• lime, alumina, silica, gypsum

Glass

• melt together minerals that can be cooled in such a way that they do not form an organised arrangement of atoms

• annealed - slow cooling

• Silica, soda, lime, alumina

Diamonds

Formation: dense form of carbon, hardest known material

Mining: kimberlite pipes

Uses: cut, grind and polish all the modern alloys and ceramics. 80% diamonds used in industry

Diamonds: formation

• form at high pressure and temp (>30kb, ~150km)

• kimberlites = igneous rock highly enriched with magnesium and volatiles (CO2 and H2))
  → of those found today onlt 3% are significantly diamondiferous
  → less than 100 have been mined

• form pipes as magma transports diamonds to the surface

• Lamproite pipes: shallower deposits

• Asteroid impacts: Popigai Russia

Gold

Formation: hydrothermal and placer deposits

Mining:

Uses: corrosion and chem resistant, most mined is still in use today. aerospace, jewellery and special alloys

Gold: Hydrothermal deposits

• hydrothermal veins associated with granitic intrustions

• gold-bearing veins move along fractures in rocks

• quartz+sulfide minerals

Gold: Placer deposits

• weatherred out from primary deposits

• concentrated through density by flowing water

• created california gold rush in 1849

Gold: famous deposit

Witwatersrand deposits

• south africa 1886

• ancient placers

• formation:
  → conglomerates laid down in shallow marine basin 2.3-2.8Ga
  → brought in by rivers from unknown primary sources in low oxygen conditions
  → associated with pyrite and uranium deposits

• Deepest: 3.5km

Rare Earth Elements

• ~169.1 ppm

• form: phosphates, silicates, carbonates, oxides and halides

• La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu

• China produces 68.6%

Primary deposits:

• Carbonatites e.g. mountain pass, usa

• Alkaline igneous rocks e.g. lovozero, russia

Secondary deposits

• Placer deposits e.g. IREL mineral sands, India

• Ion adsorption clays e.g. South China Clay Deposits

What were the key trends in global primary energy consumption in the most recent year?

Total primary energy consumption rose 2% over 2022, exceeding its 10-year average and 2019 levels. Renewables reached 14.6% of total energy (up 0.4%), and with nuclear, accounted for over 18%. Fossil fuels dropped to 81.5% of primary energy (down 0.4%).

Carbon cycle

The carbon cycle is the continuous movement of carbon among the atmosphere, oceans, soil, and living organisms. Key processes include photosynthesis, respiration, decomposition, ocean uptake, and fossil fuel combustion.

How are fossil fuels created?

• created as atmospheric CO2 formed into organic matter (C, H, O)

• 1% est of the total organic matter is preserved through burial in sediments

How is coal formed?

• dead plant matter millions of years ago form thick layer of matter

• weight of laters that form ontop increases heat and pressure

• plant matter undergoes chemical and physical changes, pushing out oxygen and leaving rich hydrocarbon deposits

what are humic coal ranks?

~10% organic matter preserved during peat forming conditions, leaves behind large hydrocarbon molecules

increase in C = decrease in H and O

State four key different coal types.

where are major coal deposits on earth?

describe how impurities cause pollution

• Clay minerals and other non-combustibles = ash

• Carbonate minerals e.g. Fe carbonate

• NH4 N2O, NO, NO2

• H2 S and FeS2 SO2

• NaCl –causes corrosion in boiler plants

• Trace elements e.g. Ge, As, U

How is oil and natural gas formed?

• tiny organisms died and were buried on ocean floor

• over time, covered by sediment and rock

• over millions of years, the remains are buried deeper and deeper

• heat and pressure turns them into oil and gas

describe the processes and depths at which oil and gas are formed

oil and gas formation with temperature

Natural gas composition

• >99% methane (CH4)

• minor ethane (C2H6)

• propane (C3H8)

• butane (C4H10)

• plus CO2 H2S N2 H2 NH3

terrestrial and marine environments

Petroleum composition

mixture of numerous hydrocarbon compounds (basis for lubricants, plus >7000 organic compounds, plus “petrol”

marine environments

reservoir rocks and their properties

porosity: void space as opposed to solid phase within a rock. Void space may be infilled by either fluids (oil, brine, etc) or gasses (atmosphere, hydrocarbons or gas)

permeability: relative ability of a material (rock) to transmit fluids through connected pore space

→ rocks with similar porosity do not necessarily have the same permeability

What are seals?

Rocks that significantly reduce the onward migration of fluids in the subsurface

Attributes:

• small pore sizes

• ductile rocks (resist fracturing)

• thich rock units with wide lateral extents

• Mudstones, evaporites, chalk and crystalline lithologies

when did oil discovery peak?

• 1960s

• today we consume ~4x as much as we discover

• oil will not run out soon, however, good quality oil will

illustrate the accumulation of oil and gas in reservoirs

What are some examples of oil extraction?

Primary = Gusher

Secondary = horsehead beam oil pumping unit, water injected to push it up

explain the enhanced oil recovery process

CO₂ EOR involves injecting carbon dioxide and water into an oil reservoir to mix with and reduce the viscosity of trapped oil, forming a miscible zone that pushes oil toward a production well for additional recovery.

How does oil refining work?

Fractional distillation:

• heating of crude oil to higher temp to condense into liquid to form useful hydrocarbons

what is natural gas composed of and how did the gas industry begin?

• gas industry began with coal gas in the early 1800s

• today it is dominated by natural gas → 80-99% methane with ethane, propane, butane, hydrogen and small amounts of CO2 and N2

Piped from wells to process plants - remove S, H2O, add “gas” smell - transmit via high pressure lines (24 km/h) Distant sources- liquefy by cooling (-162°C; 1/600 volume) and transport in ships

state some unconventional fossil fuels

• oil based
  → oil (tar) sands
  → oil shales

• Gas based
  → coalbed methane
  → shale gas

Oil shales/sands

• fine grained rocks - kerogen

• swmps and shallow marine envs

• xontains mixture of heavy hydrocarbons - can be converted to oil by heating >500C

• USA and Russia

What is Coalbed methane?

• CBM is extracted by releasing pressure in coal seams, by natural gas production or by pumping water

• most gas is adsorbed on the surface of the coal - can contain 2-3x more gas per unit of rock volume than conventional gas deposits

Shale gas

• extracted from source rock and has naturally low permeability

• gas held in frctures, pore spaces and adsorbed onto the organic material of shale

• ‘crack’ the rock using fracturing methods like ‘fracking’

Publication: Unextractable fossil fuels in a 1.5C world

To have a 50% chance of limiting warming to 1.5 °C, by 2050 about 60% of oil and fossil methane gas and 90% of coal must remain unextracted. Global oil and gas production must decline by 3% annually, with most regions reaching peak production within the decade.